Catch a boat tour from Chiapa de Corzo to see the Canyon del Sumidero. It is a spectacular ride through narrow canyons with cliff walls that rise as high as 1000 meters straight up. Along the edges you'll see crocodiles, buzzards and occasionally monkeys in the trees. It's best to go before 10am if possible, the water is calm, the light is at a good angle, and the temperature is cooler.